In recent years, there have been increasingly proposed techniques in which an operation unit is illuminated to facilitate operation of push buttons and the like even in the dark in various kinds of electronic devices, particularly potable terminals such as mobile phones and the like. In addition, there has been a need for a light guide sheet for providing a variety of illumination and a movable contact structure using the light guide sheet in order to deliver information of caller and so on to device users.
FIGS. 9 and 10 show a conventional switch using such a light guide sheet and such a movable contact structure.
In a sectional view of these figures, the dimension in a thickness direction is enlarged for the purpose of ease understandings of configuration.
FIG. 9 is a sectional view of a conventional switch. As shown in FIG. 9, a movable contact structure 4 includes an optically transparent and flexible film-shaped light guide sheet 1 having a plurality of dot-shaped illumination parts 1a formed thereon, a film-shaped base sheet 2 whose peripheral predetermined sites are attached to the bottom side of the light guide sheet 1 by means of an adhesive (not shown), and a substantially dome-shaped movable contact 3 which is formed of a conductive metal thin plate and is attached to the bottom side of the base sheet 2 under the illumination parts 1a. 
On the top side 5a of a wiring board 5 are disposed fixed contacts 6, each of which includes a circle-shaped central fixed contact 6a and horseshoe-shaped or ring-shaped outer fixed contacts 6b surrounding the central fixed contact 6a. Light emitting elements 7 such as light emitting diodes or the like are disposed on the top side 5a of the wiring board 5, and a plurality of wiring patterns (not shown) are disposed on the top side 5a and bottom side 5b of the wiring board 5.
A switch 15 is constructed by attaching the movable contact structure 4 to the top side 5a of the wiring board 5 in such a manner that the circumference of the movable contact 3 lies above the outer fixed contacts 6b and a central portion 3a of the bottom side of the movable contact 3 opposes the central fixed contact 6a with a predetermined gap therebetween.
The switch 15 as constructed above is connected to an electronic circuit (not shown) and is incorporated into a fixed housing 51 on which a plurality of dial buttons 55, an operation button 56 and a microphone 57 are disposed, for example, in a clamshell type mobile phone 50, as shown in FIG. 10. In addition, the fixed housing 51 is rotatably connected to a movable housing 52 provided with a speaker 53 and a display unit 54.
As shown in FIG. 9, each of the dial buttons 55 includes a light transmitting part 55a, a light shielding part 55b covering the light transmitting part 55a, and a display part 55c through which the light transmitting part 55a is exposed in a shape of character or symbol.
The operation button 56 is composed of a ring-shaped operation part 58 and a circle-shaped operation part 59. The ring-shaped operation part 58 is composed of a light transmitting part 58a and a light shielding part 58b contacting the light transmitting part 58a. The circle-shaped operation part 59 is composed of a light transmitting part 59a and a light shielding part 59b contacting the light transmitting part 59a. 
With the above configuration, when a dial button 55, the ring-shaped operation part 58 or the circle-shaped operation part 59 is pushed, the top side of the light guide sheet 1 is pressed by the lower end of the respective light transmitting part 55a, 58a or 59a. A substantially dome-shaped central portion 3b of the movable contact 3 is pressed accordingly. When a pressing force is applied to the movable contact 3, the movable contact 3 is elastically and inversely recessed downward, so that the central portion 3a of the bottom side of the movable contact 3 contacts the central fixed contact 6a, thereby providing electrical connection therebetween.
Conversely, when the pressing force to the dial button 55 or the operation button 56 is released, the movable contact 3 returns to its original state by elasticity, so that the central portion 3a of the bottom side of the movable contact 3 is detached from the central fixed contact 6a, thereby providing electrical isolation between the central fixed contact 6a and the outer fixed contact 6b. 
With such electrical connection/isolation of the fixed contact 6, a device is switched between its functions and power is supplied to from an electronic circuit (not shown) of the device to the light emitting elements 7, thereby emitting light from the light emitting elements 7.
The emitted light is incident from the right end side 1b of the light guide sheet 1 and propagates toward the left side while being reflected within the light guide sheet 1, with some of the light being randomly reflected and being diffused above the illumination parts 1a. Thus, the light is transmitted through each of the light transmitting parts 55a, 58a and 59a of the dial buttons 55, the ring-shaped operation part 58 and the circle-shaped operation part 59 and is diffused upward. Accordingly, top sides of the dial buttons 55, the ring-shaped operation part 58 and the circle-shaped operation part 59 are illuminated.
For example, in the clamshell type mobile phone 50 shown in FIG. 10, when a call is made using the speaker 53 and the microphone 57, light emitting elements (not shown) contained in the fixed housing 51 emit light by being supplied with power from a power source by means of an electronic circuit (not shown). Accordingly, the top sides of the dial buttons 55, the ring-shaped operation part 58 and the circle-shaped operation part 59 are simultaneously illuminated.
The display unit 54 enables display of various setting menus (not shown) of the mobile phone, for example. When a user operates the ring-shaped operation part 58 and the circle-shaped operation part 59 according to the setting menus displayed on the display unit 54, the ring-shaped operation part 58, the circle-shaped operation part 59 and the dial buttons 55 are simultaneously illuminated by means of the electronic circuit (not shown). This provides a mobile phone with high visibility and high operability even in the dark.
As one of prior art documents related to the present invention, for example, Japanese Unexamined Patent Application Publication No. 2007-87749 is known.
However, in the above-described conventional switch, the switch 15 is incorporated in the fixed housing 51 and all of the top sides of the dial buttons 55 and the operation button 56 are simultaneously illuminated with the light emitted from the light emitting elements 7. Therefore, there is a difficulty in achieving a variety of illuminations such as, for example, illuminating the dial buttons 55 and the operation button 56 at different timings.